A conventionally used method of forming independent SAW devices accommodating to a plurality of frequencies on one substrate is making a plurality of electrode patterns having the same thickness at different intervals. When a plurality of SAW devices having significantly different frequencies are formed by this method, it is extremely difficult to design and manufacture a plurality of patterns having different intervals between the electrodes under optimum conditions of each pattern.
As means of addressing this problem, the Japanese Patent Unexamined Publication No. H10-93369 discloses a method of laminating a plurality of kinds of metals having significantly different etching speeds, and forming a plurality of SAW devices having different thicknesses by utilizing the difference in etching speeds.
However, for the method of utilizing the difference in etching speeds, combinations of metals having large difference in etching speeds are limited and thus the design of electrode patterns is restricted. Additionally, when a metal film is dry-etched, a part of the metal film without a photo-resist layer is susceptible to damage. On the other hand, when a metal film is wet-etched, the side faces of the metal film are affected by the etching. Therefore, by any one of the etching methods, accurate formation of electrode patterns is difficult. For this reason, variations in frequency increase.